Automatic apparatus for supplying liquids to roller mills

ABSTRACT

An apparatus for automatically controlling the liquid level of a roller mill feed-pool embodying a pressurized vessel containing the liquid to be milled under uniform pressure and control means for regulating the pressure on the liquid to deliver the liquid to the feed-pool as required.

United States Patent Stone Feb. 22, 1972 [54] AUTOMATIC APPARATUS FOR [56] References Cited SUPPLYING LIQUIDS T0 ROLLER- UNITED STATES PATENTS MILLS 2,622,855 12/1952 Kulp et al [72] Inventor: Leslie F. Stone, Westchester, Ill. 3 490 750 1/1970 Brennan JL 2 327 448 8/1943 Olive RI hard M l P k, [73] Ass'gme c Company 6 me 2,754,068 7/1956 Ploberger ..241/222 [22] Filed: Dec. 11, 1969 Primary ExaminerGranville Y. Custer, .Ir.

L. H 1 pp No: 884,057 itgnmesy John utchmson William Lohff and Alan M 52 US. Cl ..241/34, 241/222 [571 ABSTRACT [51] Int. Cl. l ..B02c 4/28 An apparatus f automatically controlling the liquid level f a Field of Search U roller mill feed-pool embodying a pressurized vessel contain- //ea/er 5 Claims, 3 Drawing Figures P/aduc/ AUTOMATIC APPARATUS FOR SUPPLYING LIQUIDS T ROLLER MILLS This invention relates to supplying liquids to roller mills and more particularly relates to an apparatus for automatically supplying highly viscous liquids such as pasty printing inks to such roller mills.

In the preparation of various multicomponent viscous liquids such as pigment based pasty printing inks, the liquid vehicle and its solid components are conventionally processed in a roller mill. These roller mills typically comprise a-plurality of motor driven, hard surfaced rollers which rotate at differential speeds so as to apply shearing stress to the liquid material being milled. This grinds and blends the liquid and its solid components into a homogeneous mass of relatively uniform composition. In conventional operation of these roller mills, the liquid to be milled is placed on the rollers to form a feed-pool contained within the nip space defined by the upper peripheral surfaces of two adjacent rollers above the point or nip where the two adjacent rollers contact. This feedpool feeds the liquid to the mill as the two adjacent rollers rotate in a downward direction thereby removing some of the liquid as a film carried between the two rollers. This liquid film may then be directly collected as the milled product or more frequently, is first passed through successive pairs of rollers to further mill the liquid prior to being collected.

While these roller mills are essential to the preparation of many industrial products, their employment nevertheless involves certain undesirable features which adversely affect the economics of the milling operation. One of the most serious of these involves supplying or replenishing the feed-pool with the liquid to be milled during operation of the roller mill. When economic, continuous operation of the roller mills is desired, the feed-pool quite often must be replenished by manual operation. This manual or hand operation for replenishing the feed-pool, however, greatly increases the labor costs of the milling and it is typically required when the liquid being milled is particularly viscous or thixotropic and thus cannot be practically delivered to the feed port by any automatic or simple pumping operation. This is especially the case for highly colored pasty printing inks which in addition to being unamendable to pumping require a most extensive and tedious cleaning of the pumping equipment so as to prevent any color contamination of different colored ink batches.

Not only does this manual replenishing of the feed-pool result in unsatisfactory economics for the-milling operation but, additionally, it often even results in or is the cause of actual costly damage to the roller mill. For example, because of the irregularity and the unreliability involved in manually replenishing the feed-pool, quite often the entire feed-pool is consumed before being replenished which causes the mill to run in a dry state. This dry operation, however, scores the surface of the rollers and necessitates a complete shutdown of the roller mill to refinish the expensive rollers before the roller mill can be reused.

Therefore, an object of this invention is to provide an apparatus for automatically supplying liquids to the feed-pool of a roller mill. Another object is to provide an apparatus which will automatically and uniformly deliver viscous liquids such as pasty printing inks to the feed-pool without utilizing any complex pumping equipment. Still another object is to provide an apparatus which will continuously maintain a desired operating liquid height or level for the feed-pool and which additionally will automatically prevent the roller mill from operating in a dry state.

These and other objects of this invention will be apparent from the further following detailed description thereof as well as from the attached drawings.

IN THE DRAWINGS FIG. 1 is a perspective view of the apparatus of this invention in combination with a roller'mill with certain portions being broken away.

FIG. 2 is an enlarged fragmentary, partially cut away side view showing portions of two rollers of the roller mill of FIG.'1 in combination with a schematic layout of a liquid level control means of this invention.

FIG. 3 is a diagrammatic layout of a control circuit for the apparatus of this invention.

In specific reference to FIGS. I and 2, the apparatus of this invention in simple embodiment comprises in combination ,a vessel 10 containing a supply of liquid, for example, pasty printing ink, maintained under uniform pressure, such vessel 10 having a discharge port 11 in a spaced relationship to the feed-pool 12 of a roller mill 13 and a control means 14 for maintaining the desired operating liquid level or height for the feed-pool 12. In automatic operation of this apparatus, the discharge port 11 of the vessel 10 is automatically or manually opened whereupon the pressurized liquid contained within the vessel 10, for example, pasty printing ink, begins to flow through the discharge port 11 and fall onto the roller mill 13 to form the feed-pool 12. The liquid continues to fall into the feed-pool 12 through the open discharge port 11 from the vessel 10 generally at a rate greater than the withdrawal rate. As the height or liquid level of the feed-pool 12 rises as a result of the added liquid, the control means 14 respond when a predetermined desired high level is reached to reduce or decrease the pressure on the liquid in the vessel 10 so as to stop or retard delivery of the liquid through the discharge port 11 and into the feed-pool 12. Thereafter, as the level or height of the liquid decreases in the feed-pool 12 due to the continuing operation of the roller mill 13 and ultimately falls below the desired high level, the control means 14 again respond to increase the pressure on the liquid in vessel 10 so as to cause it to again flow through the discharge port 11 and fall into the feed-pool 12 to replenish the liquid being withdrawn by action of the roller mill. This control cycle then automatically repeats to continuously maintain the desired operating liquid level in the feed-pool 12.

The roller mill 13 having the feed-pool 12 which is automatically supplied or replenished'according to this invention can include any of the standard roller mills conventionally employed for milling liquids and particularly highly viscous liquids such as pasty printing inks. As simply illustrated in FIGS. 1 and 2, the rollermill 13 comprises fundamentally a plurality of rollers 15 shown in FIG. 1 as three in number. These rollers 15 are suitably supported and rotatably mounted on a roller support 16 and are driven by motor means 17. These roller support .16 and the motor means 17 are well known in the art and for purposes of simplicity and clarity their detailsare omitted herein. The rollers 15a and 15b of the roller mill 13 contact to define the nip space which holds the feed-pool 12 between the opposite adjacent peripheral surfaces 18 and 19 of the rollers 15a and 15b, respectively, above the point n where such rollers contact (FIG. 2). When necessary, the vertical sides 20 and 21 of the roller support 16 can assist in holding the feed-pool 12 by acting as restraining boundaries for the opposite ends of the feed-pool. The motor means 17 drive the roller 15a and 15b to rotate in the general direction shown by the arrows (FIG. 2) at various differential speeds to grind and blend the liquid into uniform consistency.

As the liquid is removed from the feed-pool 12 as a film.22 (FIG. 2) by the downward rotating action of the rollers 15a and 15b, the film 22 first passes on the lower peripheral surface of the roller 15b and then transfer to roller 15 whereupon it is usually recovered by the scraping action of a doctor blade 23. The milled liquid, for example, pasty printing ink, is then collected typically by falling action into an open ended container 24a. Any number of rollers 15 greater than two can, of course, be employed for the roller mill 13 depending upon the particular type of milling operation desired. However, because these roller mills as simply typified by roller mill 13 in FIG. 1 are so well known in the art, further details of the .number of rollers, types of construction material and rotation-speeds for the rollers 15 as well as other common mechanical components of the roller mills 15 are omitted herein for purposes of simplicity.

While the apparatus of this invention is directed for use during the roller milling of liquids generally, and particularly highly viscous liquids, it is particularly advantageous for employment with pasty printing inks. For this reason and for purposes of convenience, the liquid described as being milled will generally be referred to hereinafter simply as printing ink. It should be understood, of course, that such reference is for brevity only and is not intended as a limitation.

The vessel as shown embodied in FIG. 1 is preferably cylindrical and has an open end above the discharge port 11 through which a downward acting piston 24 can pass and pressure contact the viscous liquid such as printing ink contained within such cylindrical vessel. Utilization of the cylinderpiston arrangement achieves a particularly advantageous method for pressurizing the ink in the cylindrical vessel 10 so that it flows through the discharge port 11 without the necessity for any undesirable pressure pumping of the viscous liquid utilizing complex pumping equipment. In addition to providing the necessary pressure to force deliver the viscous ink through the discharge port 11, this arrangement also and most importantly applies the pressure uniformly across the surface of the ink within the vessel 10 and consequently substantially all of the ink is ultimately delivered through the port 11 by the downward movement of piston 24. Moreover, the downward and scraping movement of the piston 24 minimizes any substantial waste of the valuable printing ink which normally would result from adherence of the ink to the interior vertical wall 25 of the vessel 10 should the necessary pressure be applied, for example, by simply air pressurizing the vessel 10.

The piston 24 associated with the vessel 10 is downward driven by rod 26 which in turn is interconnected to a piston (not shown) internal to pneumatic cylinder 27 of conventional design. Pneumatic cylinder 27 is suitably operated by compressed air to move the piston 24 either up or down and advantageously is double acting. The compressed air is delivered to cylinder 27 for downward movement via conduit 28 which communicates with compressed air supply conduit 29 through air valve 30 controlled by solenoid 31, both such valve and solenoid being of conventional design. The air valve 30 can also be manually operated to lower the piston 24 into pressure engaging contact with the ink at the start of the milling operation as hereinafter more fully explained. The cylinder 27 is supported in fixed position in a spaced relationship to the vessel 10 by overhead suspended frame 32a which together with the piston 24 and rod 26 are so designed and arranged that the piston 24 can be retracted upwardly to completely disengage from the vessel 10 by suitable automatic or manual operation of air valve 30a allowing air to flow into cylinder 27 via conduit 30b from air supply conduit 29. This disengagement of the piston 24 from the vessel 10 allows the vessel 10 to be readily moved away from its spaced position in relation to the feed-pool 12 of the roller mill 13 via transport means 32 which, as illustrated in FIG. 1, simply comprises a roller conveyor 33 of conventional design consisting essentially of rollers 34 mounted on a frame 35 supported by legs 36.

'With this ready mobility for the vessel 10, a second vessel (not shown) ofidentical design containing a new supply of ink of the same or different color can be quickly and simply exchanged for the vessel 10 upon depletion of its ink supply. Not only does this allow for a quick supply of additional ink but it achieves an instantaneous interchangeability of inks of different color without the need for any equipment shutdown to extensively clean the ink feeding equipment. In the installation of the second vessel (not shown) because the piston 24 remains in a fixed position, the second ink containing vessel can simply be moved via transport means 32 into piston-engaging position below the raised piston 24 and then the piston 24 can be lowered by suitable manual operation of air valve 30 controlling cylinder 27 to bring the piston downwardly into uniform pressure contact with the ink in such second vessel. So as to minimize the possibility of any color contamination of the ink in the second vessel by intermixing with any ink of the previous vessel remaining on the ink-contacting surface of the piston 24, a discardable protective cover 37, for example, a

plastic sheet, may be inserted over the ink-contacting surface and simply may be replaced for each new vessel of ink.

The discharge port 11 for the vessel 10 as indicated, can be opened or closed either by manual or automatic operation. In simple arrangement as shown in FIG. 1, the discharge port 11 simply comprises an aperture through the wall of cylindrical vessel 10. This aperture of the port 11 is suitably rectangular in cross section and advantageously located at a lower position of the vessel 10 so as to maximize full delivery of substantially all of the ink upon the downward compressive movement of the piston 24. The opening and closing of the port 11 can be achieved by various conventional methods with a preferred closing operation being achieved through employment of a slidable gate 38 movable over the discharge port 11. The opening and closing of the discharge port 11 achieved by the sliding action of the gate 38 allows a quick movement which achieves in its closing movement a guillotine-type cutting action to actually sever and cut the highly viscous ink and thus prevent any substantial dribbling or trickling of the ink during exchange of the vessels 10 on the transport means 32. The gate 38 is suitably held and guided by guides 39 which are integral with the cylindrical vessel 10 and engage the vertical edges of the gate 38 to secure and direct its sliding movement over the port 11.

The control means 14 for maintaining the desired height or liquid level for the feed-pool 12 by regulation of the pressure on the ink in the vessel 10 can include various different apparatus for sensing and regulating liquid heights and for applying pressure on the ink. However, a particularly preferred control means 14 especially for use in combination with the cylindrical vessel 10 is schematically illustrated in FIG. 2. The control means 14, as shown and as described in my copending application Ser. No. 884,301 filed Dec. 1 l, 1969 entitled Liquid Level Controller, suitably include a probe 40 which extends into the feed-pool 12 to a desired elevation or high level. The probe 40 is connected to pressure-regulating means 41 and when the liquid level of the feed-pool 12 is below the desired high level, the probe 40 senses this condition and in response actuates the pressure-regulating means 41 to increase the pressure on the ink in the vessel 10 by a downward compressive movement of piston 24. This causes the thus pressurized ink to flow through the open discharge port 11 and fall into the feed-pool 12 to replenish the ink which is being withdrawn therefrom by the operation of the roller mill 13. When the level of the ink in the feed-pool 12 rises due to the addition of the ink from the vessel 10 and exceeds the predetermined high level, the probe 40 again senses this condition and actuates the pressure-regulating means 41 to decrease the pressure on the ink in the vessel 10 thus stopping or retarding delivery of the viscous ink through the discharge port 11 and into the feedpool 12.

The probe 40 in simple embodiment comprises a pneumatic hollow tube of relatively small diameter and of suitable construction material through which air under a relatively low pressure freely flows. The probe 40 can be of unitary construction or suitably include flexible joints (not shown) so as to allow the probe 40 to be universally moved to any elevation or position in the feed-pool 12 so that a terminal opening 42 of the probe 40 (FIG. 2) corresponds to a particularly desired high level for the feed-pool 12. Air is charged to the probe 40 via conduits 43 and 44a from air pressure supply conduit 29 controlled by reducing air valve 44. In addition to controlling admittance of air to the probe 40, the air valve 44 also simultaneously reduces the air to a very low pressure in the order of approximately 1 pound per square inch. Alternatively, if such a pressure reduction function is not desired for air valve 44, then a suitable orifice restriction (not shown) can be located internal the conduit 44a leading to the probe 40 downstream from the valve 44 to achieve the desired low air pressure.

A particularly advantageous feature of the probe 40 is that because of its simple structure, it can be readily and quickly cleaned by simply wiping or washing any liquid remaining on the probe after a milling operation. This is especially desirable when milling such viscous material as highly colored printing inks and allows quick use of the roller mill for different color inks after a simple cleaning of the rollers and probe 40 without any danger of color contamination.

When the liquid height or level of the feed-pool 12 is below the predetermined high level, the air passing through the probe 40 exits freely out of the terminal opening 42 of the probe 40 thus maintaining the air pressure in the probe 40 within the low range or at a low-pressure condition set by the air valve 44. This low air pressure condition within the probe 40 actuates the pressure regulating means 41 as previously described to initiate a downward movement of piston 24. The pressure regulating means 41 conveniently include a pressure actuated switch 45 communicating with the probe 40 through air conduit 45a and the solenoid 31 controlling air valve which when open, admits air to the cylinder 27 to move the piston 24 downward. In operation of the pressure regulating means 41, when the air pressure in the probe 40 is at a low air pressure condition signifying that the terminal opening 42 of the probe 40 is free of any ink covering and hence that the ink level is below the desired high level, the pressure switch 45 is actuated. This pressure switch 45 is of conventional design and has internal switch contacts (not shown) which are adapted to close at a particular low pressure and to open at a higher pressure. The contacts of the pressure-sensitive switch 45 are in series with the solenoid 31 of conventional design via lead 53 and when the low-pressure condition of the probe 40 closes the pressure-sensitive switch 41, the solenoid 31 is energized, Upon being so energized, the solenoid 31 opens the air valve 30 allowing pressurized air to flow from air pressure supply conduit 29 via conduit 28 into cylinder 27 thus moving piston 24 downwardly into pressure contact with the ink in vessel 10. This causes the pressurized ink to flow through the discharge port 11 and fall into the feed-pool 12.

The reverse of this control procedure occurs when the level of the liquid in the feed-pool rises above the high level of the feed-pool l2 determined by the position or elevation of the terminal opening 42 of the probe 40. When the liquid level rises above the high level, the terminal opening 42 is closed or sealed by the viscous ink in the feed-pool 12 whereupon the air pressure within the probe 40 increases and ultimately reaches a high pressure or high-pressure condition which actuates the pressure switch 41 to open its contacts and thus deenergize the solenoid 31. Upon being so deenergized, the solenoid 31 moves the air valve 30 to a closed position thereby releasing the air pressure to cylinder 27 which stops the downward movement of the piston 24. This, in turn, releases or relieves the pressure on the ink in the vessel 10 which terminates delivery of the viscous ink through the discharge port I1 and into the feed-pool repeats This control cycle repreats continuously as the level of the feed-pool 12 rises and falls during operation of the roller mill 13 thus maintaining and controlling the desired operational height of the liquid in the feed-pool 12.

Because the liquid in the feed-pool 12 is typically quite thick or viscous, it readily seals the terminal opening 42 of the probe 40 thus preventing any substantial release of the air from the probe 40 by bubbling through the liquid. Thus, the pressure within the probe 40 quickly rises to a high-pressure condition to actuate the pressure switch 45. This renders the pressure regulating means 41 quite sensitive to any rise of the li uid level in the feed-pool 12. To insure that the probe is equally sensitive to any lowering of the feed-pool level, the minimum air pressure maintained within the probe 40 by means of air valve 44 and its associated internal orifice restrictions, if any, should be sufficient so as to blow off any viscous liquids adhering to the terminal opening 42 of the probe 40 when the liquid level of the feed-pool 12 falls below the terminal opening 42. This necessary clearing of the terminal opening 42 is, however, automatically assisted by the highpressure condition of the probe 40 created by the sealing action of the liquid. For example, when the liquid level falls, the high pressure within the probe 40 will provide a surge of pressure to purge the terminal opening 42 and remove any adhering liquid.

As an associated and preferred feature of the control means 14, a second probe 46 extends into the feed-pool 12 to a predetermined low level. This low level corresponds to a predetermined liquid height or level considered to be the minimum safe operating level for the feed-pool 12. This low level probe 46 is analogous to the high-level probe and air under relatively low pressure is admitted to probe 46 from air regulating valve 44 via conduit 43 and conduit 47 having an internal restriction (not shown) to prevent any pressure condi- .tion within probe 46 from affecting any pressure condition within the probe 40. This probe 46 is connected to motor regulating means 48 which include a pressure-sensitive switch 49 communicating with the probe 46 via air conduit 49a. Pressure-sensitive switch 49 is similar to pressure-sensitive switch and its switch contacts (not shown) are set so that the switch 49 is in open position at a particular high-pressure condition within the probe 46 and closed at a particularly lowpressure condition. The contacts of pressure-sensitive switch 49 as more fully explained hereinafter, are in series with a relay having contacts in series with the motor means 17 which drive the rollers 15.

When the ink in the feed-pool 12 is above the low level determined by the position of the terminal opening 50 of the probe 46, the terminal opening is closed by the liquid in the feed-pool 12 thereby creating a high-pressure condition within the probe 46. This high-pressure condition maintains the pressure-sensitive switch 49 in an open position which allows the motor means 17 to remain energized and drive the rollers 15. When, however, the ink level falls below the desired low level for the feed-pool 12, the terminal opening 50 of the probe 46 is uncovered thus causing the pressure within the probe 46 to fall to a low-pressure condition. Upon the lowering of the air pressure in the probe 46, the pressure switch 49 contacts close, thus deenergizing the motor means 17 and thereby stopping the roller mill 13. The employment of this low level probe 46 thus automatically prevents the roller mill 13 from ever running in a dry state as the result of the feed-pool 12 being totally consumed by operation of the roller mill 13 without being replenished with additional ink from the vessel 10.

The control means 14, pressure regulating means 41 and the motor-regulating means 48 are preferably electrically operated, and their various components (not shown) may be suitably housed in a control box 51a. The wiring interconnecting the various components with the apparatus of this invention are not completely shown in FIGS. 1 and 2 for purposes of convenience. The operation of the control circuits is best described in reference to FIG. 3.

Assuming at the start of the milling operation the discharge port 11 of the vessel 10 is opened either manually or automatically by raising gate 38. The valve 30 is manually operated so as to lower the piston 24 downward and bring it into pressure contact with the ink contained within the vessel 10. A line switch 51 is then moved to a closed position which connects the apparatus of this invention to a suitable power source, L1 and L2, for example, l10 volts, 60 cycles. On the closing of the line switch 51, a circuit is completed from lead 52 via lead 53 and pressure-sensitive switch 41, when closed, to energize solenoid 31 having returned to source via leads 54 and 55. As previously explained, when solenoid 31 is energized, the piston 24 controlled by cylinder 27 pressurizes the ink by downward movement causing the ink to uniformly flow through the open discharge port 11 and fall onto rollers 15a and 15b to form the feed-pool 12. 1

Motor switch 54 is then moved to a closed position thus completing via leads 52 and 55 and normally closed switch contact 56, an energizing circuit through motor means 17 having returned to source via leads 57 and 55. The motor means 17, being so energized, then turn the rollers 15 removing a portion of the liquid in the feed-pool as film 22 at a removal rate slower than the addition rate of the ink from the vessel 10.

As the level of the ink in the feed-pool l2 rises above the terminal opening 42 of probe 40 by the addition of the ink from the vessel 10, the terminal opening 42 is closed by the sealing action of the liquid to increase the pressure within the probe 40 to a high-pressure condition. This high-pressure condition actuates the pressure-sensitive switch 41, opening such switch and thereby interrupting the energizing circuit to the solenoid 31. Upon being deenergized, the solenoid 31, by control of air valve 30, releases the air pressure to cylinder 27 thus stopping the downward compressive movement of piston 24 and hence, the delivery of the ink to the feed-pool 12. As previously explained, the reverse operation occurs when the level in the feed-pool l2 falls below the terminal opening 42 of the probe 40. This creates a low-pressure condition within the probe 40 which actuates the pressure-sensitive switch 41 to move to a closed position which again completes an energizing circuit to solenoid 31 causing the ink to once again flow under pressure through the discharge port 11.

with the level of the feed-pool 12 above the low level determined by the elevation of the terminal opening 50 of the probe 46, the air pressure in such probe is maintained at a high-pressure condition which maintains the pressure-sensitive switch 49 in open position. When the level of the feed-pool 12 should fall before the terminal opening 50 of the probe 46, for example, when the ink supply in the vessel is exhausted, the high-pressure condition within the probe 46 is released thereby causing a low-pressure condition which actuates the pressure-sensitive switch 49 to a closed position. When the switch 49 is in a closed position, a circuit is completed via leads S3 and 58 to energize in parallel a time delay relay 59 and an alarm 60 having a return to source via leads 61 and 55. Upon being energized, the alarm associated, for example, with a bell or a light (not shown) signals the operator to shut down the roller mill 13 by opening motor switch 54 and line switch 51 and thereafter replacing vessel 10 with a second vessel 10 having a new supply of ink. As a feature of automatic safety, should the operator not respond to the alarm 60, the time delay relay 59, after a suitable time delay upon being energized, opens its contact switch 56 which is in series with the motor means 17. Upon the opening of the contact switch 56, the energizing circuit to the motor means 17 is interrupted thereby deenergizing the motor means 17 and stopping the roller mill 13. This feature, as previously discussed, automatically prevents any scoring of the rollers which would necessitate shutdown of the roller mill [3 for extensive repairs to reface the rollers 15 should the roller mill 13 be permitted to operate without liquid in the feed-pool 12.

l claim:

1. An apparatus for automatically supplying liquid to a roller mill of the type having at least two closely spaced rotatable rollers driven by motor means and adapted to hold a feedpool of the liquid in the nip space between the upper adjacent surfaces of the two rollers which comprises in combination a vessel containing a supply of the liquid maintained under uniform pressure across its upper surface, such vessel having a discharge port in a spaced relationship to the feed-pool and control means for maintaining a desired liquid level in the feed-pool by regulating the pressure within the vessel which forces the liquid from the vessel through the discharge port to the feed-pool wherein the control means include a pneumatic probe communicating with pressure regulating means and extending into the feed-pool to a predetermined high level, such probe being open when the liquid level of the feed-pool is below the high level to actuate the pressure regulating means to cause liquid to flow from the vessel to the feed-pool and such probe being closed by the liquid in the feed-pool when the liquid level is above the high level to actuate the pressureregulating means to stop the flow ofliquid from the vessel.

2. The apparatus of claim 1 wherein the control means include a second pneumatic probe communicating with motor regulating means and extending into the feed-pool to a predetermined low level, such second probe being closed by the liquid in the feed-pool when the liquid level of the feedpool is above the low level to actuate the motor regulating means to allow the motor means to drive the rollers and such probe being open when the liquid level is below the low level to actuate the motor-regulating means to stop the rollers.

3. An apparatus for automatically supplying liquid to a roller mill of the type having at least two closely spaced rotatable rollers driven by motor means and adapted to hold a feedpool of the liquid in the nip space between the upper adjacent surfaces of the two rollers which comprises in combination a cylindrical vessel containing a supply of the liquid and associated with a piston which maintains a uniform pressure across the surface of the liquid within the vessel by a downward compressive movement with such piston being controlled by pressure-regulating means, such vessel having a discharge port in a spaced relationship to the feed-pool and control means for maintaining a desired liquid level in the feed-pool by regulating the pressure within the vessel which forces the liquid from the vessel through the discharge port to the feed-pool wherein the control means include a pneumatic probe communicating with the pressure regulating means and extending into the feed-pool to a predetermined high level, such probe being open when the liquid level of the feed-pool is below the high level to actuate the pressure-regulating means to cause the piston to move downwardly thereby pressurizing the liquid in the cylindrical vessel to flow through the discharge port and fall into the feed-pool and such probe being closed by the liquid in the feed-pool when the liquid level is above the high level to actuate the pressure-regulating means to stop the downward movement of the piston thereby releasing the pressure on the liquid in the vessel and stopping its flow through the discharge port into the feed-pool.

4. The apparatus of claim 3 wherein the pressure-regulating means are electrically operated and include a pressure-sensitive switch communicating with the probe, such switch being in series with a solenoid controlling the air pressure in a cylinder for moving the piston, such switch being actuated to close by a low-pressure condition within the probe when the liquid level is below the high level whereby a circuit is completed to energize the solenoid to admit air to the cylinder to move the piston downwardly and such switch being actuated to open by a high-pressure condition within the probe when the liquid is above the high level whereby the circuit energizing the solenoid is interrupted thereby releasing the air pressure in the cylinder to stop the downward movement of the piston.

5, An apparatus for automatically supplying liquid to a roller mill of the type having at least two closely spaced rotatable rollers driven by motor means and adapted to hold a feedpool of the liquid in the nip space between the upper adjacent surfaces of the two rollers which comprises in combination a cylindrical vessel containing a supply of the liquid and associated with a piston which maintains a uniform pressure across the surface of the liquid within the vessel by a downward compressive movement with such piston being controlled by pressure-regulating means, such vessel having a discharge port in a spaced relationship to the feed-pool and control means for maintaining a desired liquid level in the feed-pool by regulating the pressure within the vessel which forces the liquid from the vessel through the discharge port to the feed-pool.

UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 3,643,876 February 22, 1972 Leslie F. Stone It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below.

On the cover sheet, the figure shown at the bottom of the Abstract should appear as shown below Column 5, line 52, feed-pool repeats should read --feed-p0ol 12.

Signed and sealed this 4th day of July 1972.

[SEAL] Attest: EDWARD M. FLETCHER, JR., ROBERT GoTTsoHALK, Gammissz'oner of Patents.

Attestmg Oficer. 

1. An apparatus for automatically supplying liquid to a roller mill of the type having at least two closely spaced rotatable rollers driven by motor means and adapted to hold a feed-pool of the liquid in the nip space between the upper adjacent surfaces of the two rollers which comprises in combination a vessel containing a supply of the liquid maintained under uniform pressure across its upper surface, such vessel having a discharge port in a spaced relationship to the feed-pool and control means for maintaining a desired liquid level in the feed-pool by regulating the pressure within the vessel which forces the liquid from the vessel through the discharge port to the feed-pool wherein the control means include a pneumatic probe communicating with pressure regulating means and extending into the feed-pool to a predetermined high level, such probe being open when the liquid level of the feed-pool is below the high level to actuate the pressure regulating means to cause liquid to flow from the vessel to the feed-pool and such probe being closed by the liquid in the feed-pool when the liquid level is above the high level to actuate the pressure-regulating means to stop the flow of liquid from the vessel.
 2. The apparatus of claim 1 wherein the control means include a second pneumatic probe communicating with motor regulating means and extending into the feed-pool to a predetermined low level, such second probe being closed by the liquid in the feed-pool when the liquid level of the feed-pool is above the low level to actuate the motor regulating means to allow the motor means to drive the rollers and such probe being open when the liquid level is below the low level to actuate the motor-regulating means to stop the rollers.
 3. An apparatus for automatically supplying liquid to a roller mill of the type having at least two closely spaced rotatable rollers driven by motor means and adapted to hold a feed-pool of the liquid in the nip space between the upper adjacent surfaces of the two rollers which comprises in combination a cylindrical vessel containing a supply of the liquid and associated with a piston which maintains a uniform pressure across thE surface of the liquid within the vessel by a downward compressive movement with such piston being controlled by pressure-regulating means, such vessel having a discharge port in a spaced relationship to the feed-pool and control means for maintaining a desired liquid level in the feed-pool by regulating the pressure within the vessel which forces the liquid from the vessel through the discharge port to the feed-pool wherein the control means include a pneumatic probe communicating with the pressure regulating means and extending into the feed-pool to a predetermined high level, such probe being open when the liquid level of the feed-pool is below the high level to actuate the pressure-regulating means to cause the piston to move downwardly thereby pressurizing the liquid in the cylindrical vessel to flow through the discharge port and fall into the feed-pool and such probe being closed by the liquid in the feed-pool when the liquid level is above the high level to actuate the pressure-regulating means to stop the downward movement of the piston thereby releasing the pressure on the liquid in the vessel and stopping its flow through the discharge port into the feed-pool.
 4. The apparatus of claim 3 wherein the pressure-regulating means are electrically operated and include a pressure-sensitive switch communicating with the probe, such switch being in series with a solenoid controlling the air pressure in a cylinder for moving the piston, such switch being actuated to close by a low-pressure condition within the probe when the liquid level is below the high level whereby a circuit is completed to energize the solenoid to admit air to the cylinder to move the piston downwardly and such switch being actuated to open by a high-pressure condition within the probe when the liquid is above the high level whereby the circuit energizing the solenoid is interrupted thereby releasing the air pressure in the cylinder to stop the downward movement of the piston.
 5. An apparatus for automatically supplying liquid to a roller mill of the type having at least two closely spaced rotatable rollers driven by motor means and adapted to hold a feed-pool of the liquid in the nip space between the upper adjacent surfaces of the two rollers which comprises in combination a cylindrical vessel containing a supply of the liquid and associated with a piston which maintains a uniform pressure across the surface of the liquid within the vessel by a downward compressive movement with such piston being controlled by pressure-regulating means, such vessel having a discharge port in a spaced relationship to the feed-pool and control means for maintaining a desired liquid level in the feed-pool by regulating the pressure within the vessel which forces the liquid from the vessel through the discharge port to the feed-pool. 